Filter

ABSTRACT

A filter unit for filtering particulates and other foreign matter from a fluid supply, comprising a filtering chamber. At least a portion of an exterior of the filtering chamber being provided with a mesh through which fluid may enter the filtering chamber in use. The mesh being sized to filter particulates and other foreign matter from the fluid. The filter unit further comprising an outlet through which filtered fluid exits the filter unit, and a rotatable member located within the filtering chamber, the rotatable member having at least one outlet spaced from an internal face of a mesh. The axis of rotation of the rotatable member being such that the at least one outlet traverses at least a substantial portion of the internal face of a mesh. The filter unit further comprising a dedicated pump having an inlet communicating with the filtering chamber and an outlet communicating solely with the rotatable member such that operation of the pump causes filtered fluid from within the filtering chamber to be pumped through the rotatable member to exit the at least one outlet and impinge on the internal face of the mesh so as to cause particulates and other foreign matter located on an external face of the mesh to be dislodged.

[0001] The present invention relates to a filter unit for filteringparticulates and other foreign matter from a fluid supplies. Inaddition, the invention relates to filter unit assemblies and filtrationsystems and methods of filtration using the filter unit.

[0002] It is known to provide filter units and filtration systems inwater supplies in order to remove particulate matter and other foreignmatter from the water supply. One example of the use of such a filterunit and filtration system is in filtering the water supply for a fishpond or aquarium.

[0003] It is known to filter a water supply by passing the water supplythrough a small aperture mesh to thereby remove particles and foreignmatter having a diameter greater than the aperture size of the mesh.However, a problem with such a system is that the mesh quickly becomesblocked with the particles and foreign matter removed from the watersupply at which point the filtration system ceases to function and thewater supply is substantially cut-off. It is therefore necessary toregularly clean the meshes of such filtration systems. This processnormally involves dismantling the filtration system which is bothtime-consuming and complicated. In addition, during maintenance of thesystem, the water supply must be cut off.

[0004] GB 2 293 333 proposes one solution to such a problem wherein afiltering chamber is provided surrounded by a small aperture mesh. Wateris drawn through the unit and through the mesh and out of an outlet pipeby means of a pump. A tapping of filtered water from the pumped outletof the filter chamber is then diverted via a return conduit into a backwashing nozzle assembly in the form of a rotatable impeller. The wateris spread from outlets of the impeller against the interior face of themesh in the hope of dislodging particles and debris on the exterior faceof the mesh. However, the device of GB 2 293 333 suffers from a numberof drawbacks. Firstly, the filter is only useable with an activelypumped filtration system. In other words, the filter unit cannot be usedwith a gravity-fed system which is commonly found in larger aquaria andfish ponds. Secondly, in order to produce a sufficient dislodging forceof the water from the impeller, it has been found necessary to divert avery significant proportion of the filtered water from the outlet backinto the rotatable impeller. Potentially up to 90% of the water pumpedthrough the filter unit must be diverted back to the rotatable impeller.Even then, the minimum pore size of the mesh which may be used with sucha filter is restricted to greater than about 250 microns otherwise thepressure drop across the filter unit becomes too great and thevolumetric throughput of the filter unit becomes too low.

[0005] The present invention aims to provide a filter unit whichovercomes the disadvantages of known devices.

[0006] Accordingly, the present invention provides a filter unit forfiltering particulates and other foreign matter from a fluid supply,comprising a filtering chamber, at least a portion of an exterior of thefiltering chamber being provided with a mesh through which fluid mayenter the filtering chamber in use, the mesh being sized to filterparticulates and other foreign matter from the fluid, the filter unitfurther comprising an outlet through which filtered fluid exits thefilter unit, and a rotatable member located within the filteringchamber, the rotatable member having at least one outlet spaced from aninternal face of a mesh, the axis of rotation of the rotatable memberbeing such that the at least one outlet traverses at least a substantialportion of the internal face of a mesh, the filter unit furthercomprising a dedicated pump having an inlet communicating with thefiltering chamber and an outlet communicating solely with the rotatablemember such that operation of the pump causes filtered fluid from withinthe filtering chamber to be pumped through the rotatable member to exitthe at least one outlet and impinge on the internal face of the mesh soas to cause particulates and other foreign matter located on an externalface of the mesh to be dislodged.

[0007] The present invention also provides a filter unit assemblycomprising a filter unit as provided above and a tank housing in whichthe filter unit is located, the tank housing being provided with aninlet for entry of fluid into the tank unit and the outlet of the filterunit forming the outlet of the tank housing.

[0008] The present invention further provides a filtration systemcomprising one or more filter units assemblies as provided above.

[0009] The present invention further provides a method of filteringfluid to remove particulates and other foreign matter comprising thesteps of passing the fluid through a filtering chamber having a meshsized to filter the particulates and other foreign matter from thefluid, outputting the fluid from the filtering chamber through an outletof the filtering chamber, wherein a dedicated pump is used to pump fluidfrom the filtering chamber exclusively through a rotatable memberlocated within the filtering chamber to exit through at least one outletof the rotatable member to impinge on an interior face of the mesh so asto dislodge particulates and other foreign matter located on an exteriorface of the mesh.

[0010] The present invention further provides a filtration system forfiltering particulates and other foreign matter from a fluid supply,comprising a tank with an inlet and an outlet, a filtration unit throughwhich fluid must pass to reach the outlet, and a sump in whichparticulates and other foreign matter from the fluid accumulates, thesump having an outlet, a drainage conduit communicating with the outlet,a pump for withdrawing fluid and accumulated particulates and otherforeign matter through the outlet and discharging it to a drainageconduit, and a programmable controller for operating a valve and pump.

[0011] Embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings inwhich:

[0012]FIG. 1 is a side elevation of a filter unit in accordance with thepresent invention;

[0013]FIG. 2 is a further side elevation of the filter unit of FIG. 1with certain parts omitted for clarity;

[0014]FIG. 3 is a cross-sectional elevation of the filter unit of FIG.1, again with certain parts omitted for clarity;

[0015]FIG. 3a is a cross-sectional elevation of an alternative filterunit, again with certain parts omitted for clarity;

[0016]FIG. 3b is a plan view of the filter unit of FIG. 3a;

[0017]FIG. 4 is a top plan view of the filter unit of FIG. 1, showinghidden components in broken lines;

[0018]FIG. 5 is a cross-sectional detail of part of the filter unit ofFIG. 3;

[0019]FIG. 6 is a cross-sectional detail of another part of the filterunit of FIG. 3;

[0020]FIG. 6b is a cross-sectional detail of an alternative part to thatof FIG. 6;

[0021]FIG. 7 is a cross-section detail of a further part of the filterunit of FIG. 3;

[0022]FIG. 8 is a side elevation of a rotor as used in the filter unitof FIG. 1;

[0023]FIG. 9 is a top plan view of the rotor of FIG. 8;

[0024]FIG. 9a is a top plan view of an alternative rotor;

[0025]FIG. 10 is a perspective view of a detail of the rotor of FIG. 8;

[0026]FIG. 11 is a top plan view of an inlet conduit as used in thefilter unit of FIG. 1;

[0027]FIG. 12 is a cross-sectional side elevation of the inlet conduitof FIG. 11;

[0028]FIG. 13 is a schematic elevation of the filter unit of FIG. 1 in afirst type of tank housing;

[0029]FIG. 13a is a schematic elevation of another filter unit assemblyin accordance with the present invention;

[0030]FIG. 13b is a schematic elevation of another filter unit assemblyin accordance with the present invention;

[0031]FIG. 14 is a schematic elevation of the filter unit of FIG. 1 in asecond type of tank housing;

[0032]FIG. 15 is a schematic elevation of the filter unit of FIG. 1 in athird type of tank housing connected to a biological cleaning stagehousing;

[0033]FIG. 16 is a schematic elevation of a plurality of the filterunits of FIG. 1 in a vertical stack formation; and

[0034]FIG. 17 is a schematic elevation of an alternative tank housing inaccordance with the present invention;

[0035]FIG. 17a is a schematic elevation of an alternative tank housingin accordance with the present invention;

[0036]FIG. 17b is a schematic elevation of another alternative tankhousing in accordance with the present invention; and

[0037]FIG. 18 is a cross sectional view of another filtration unit inaccordance with the present invention; and

[0038]FIG. 19 is a schematic view of a filtration system in accordancewith the present invention.

[0039] Referring to FIGS. 1 to 3, a filter unit 1 in accordance with thepresent invention comprises a filter unit housing 10 having circularupper and lower covers 11, 12. A mesh 13 extends around thecircumference of the filter unit housing 10 extending between the uppercover 11 and lower cover 12. The upper cover 11, lower cover 12 and mesh13 together define a cylindrically shaped filter chamber 9.

[0040] Preferably the materials of the filter unit, except whereotherwise mentioned, are made of stainless steel grade 316.

[0041] An outlet 15 is provided at a centre of the filter chamber 9 inthe lower cover 12. A rubber sleeve 16 located at an end of the outlet15 allows the outlet of the filter chamber 9 to be connected to a pipeor other conduit of varying diameter from approximately 7.5 cm to 15 cm.

[0042] Referring to FIGS. 3 to 7, the mesh 13 is mounted to the uppercover 11 and lower cover 12 by means of tie brackets 33. Each tiebracket 33 comprises an elongated strip of metal having an inturnedflange at either end. The mesh 13 is spot welded to a number of tiebrackets 33. The mesh and tie bracket assembly is then connected to theupper cover 11 and the lower cover 12 by virtue of bolts 28, 26. A‘fluidtight’ seal is provided by annular seals 20, 27 provided inannular channels 34, 35 formed in the upper cover 11 and lower cover 12respectively. As seen in FIGS. 5 to 7, the mesh 13 protrudes into theupper and lower seals 27, 20 to form an improved connection. As a resultfluid can only enter the filter chamber 9 through the mesh 13.

[0043] An alternative seal is illustrated in FIG. 6b wherein the annularchannel is dispensed with. Instead an enlarged gasket or o-ring 20′ isprovided which is sandwiched between the tie bracket 33 and lower cover12 as the bolt 26 is fastened. As a result the O-ring 20 bulges outwardsto form a face seal against the mesh 13. This seal may be used on theupper and lower covers 11, 12.

[0044] The mesh 13 is also made of stainless steel grade 316. Theaperture size of the mesh 13 can be varied depending on the requireddegree of filtration. However, in accordance with the present inventionaperture sizes of 200 microns or less can be utilised. One form of mesh13 is a Hollander weave mesh of aperture size 100 microns. The Hollanderweave construction has been found to offer good resistance to workhardening and fatigue failure. Other mesh types such as wedge wirescreen (also known as triangular bar screen) and plain weaves may beused. The mesh 13 may also be made of nylon of a suitable thickness.

[0045] A rotatable member in the form of a rotor 14 is provided withinthe filter chamber 9 having an axis of rotation which is substantiallyvertical and coincident with the major axis of the cylindrical filterchamber 9. The rotor 14 is mounted to the upper cover 11 and lower cover12 by bolts.

[0046] Referring to FIGS. 8 to 10, the rotor 14 of the filter unit 1comprises a vertically orientated hollow rotor shaft 21 and a hollowrotor arm 22 which extends substantially perpendicular thereto.Preferably, the rotor arm 22 and rotor shaft 21 are welded together. Ateach distal end of the rotor arm 22, there is provided a rotor nozzle23. Each rotor nozzle 23 comprises an outlet 29 which is angled at anangle a (alpha) to a radial direction 36 passing coincident to the rotorarm 22 as shown in FIG. 9. Angle a may be varied substantially 0 and 90degrees. Preferably, a is between 35 and 50 degrees. In one example thetwo outlets 29 are both set with an α of 45 degrees. The two outlets 29may be set at different angles; for example, one outlet may have an α of35 degrees and the other 50 degrees. Alternatively, one of the outletsmay be at 0 degrees and the other outlet at an angle greater than 0degrees.

[0047] Alternatively, as shown in FIG. 9a, the nozzle outlets 29 may beset at 0 degrees and one or more openings 29 a provided in the sidewalls of the nozzle 23 through which a proportion of the water passes inorder to rotate the rotor 14.

[0048] A pump 17 is provided attached to an exterior of the filter unithousing 10. An inlet of the pump 17 is connected to an interior of thefilter chamber 9 by means of an aperture 32 in the lower cover 12 (asshown in FIG. 4). An outlet of the pump 17 connects solely to the rotor14 via an aperture 31 in the lower cover 12 and an inlet conduit 19. Thepump 17 is consequently dedicated to supplying water to rotor 14.

[0049] The pump 17 is preferably an electric pump powered by an externalpower source. The pump has a rating of greater than 2,000 litres perhour and preferably greater than 4,000 litres per hour. One example of asuitable pump is the ‘Nautilus 6,000’ pump manufactured by Oase having arating of 6,000 litres per hour.

[0050] Referring to FIGS. 11 and 12, the inlet conduit 19 of the filterunit 1 is provided with a first aperture 31 a and a second aperture 30a. When positioned in the filter unit 1, the first aperture 31 acoincides with the aperture 31 in the lower cover which provides aconnection with the outlet of the pump 17. Likewise, the second aperture30 a is coincident with a base of the hollow rotor shaft 21. As such,the outlet of the pump 17 communicates with the interior of the rotor 14via the pump outlet aperture 31, aperture 31 a, internal conduit 19,aperture 30 a and rotor shaft 21.

[0051] An air bleed valve 18 is provided in upper cover 11 to allow airtrapped in the filter unit 1 during installation to be bled off.

[0052] The use of the filter unit 1 will now be described by way ofexample only and for clarity for use with water. However, other fluids,being liquids or gases, may be filtered using the present invention.

[0053] The filter unit 1 is installed in use in a tank housing 40 toform a filter unit assembly. FIG. 13 shows a first type of tank housing40 which comprises an inlet 41 located at or near a top of the tankhousing 40, an outlet pipe 42 and a sump 43 provided with a bottom drainline 44. The filter unit 1 is installed in the tank housing 40 with theoutlet 15 being connected to the outlet pipe 42 by means of the rubbersleeve 16 and a jubilee clip. The tank housing 40 is then filled withwater from inlet 41. During this stage the bleed valve 18 may beoperated to remove any air trapped in the filter unit 1.

[0054] In operation, there is a flow of water from the inlet 41 to theoutlet pump 42 such that the filter unit 1 is surrounded by water to befiltered. Advantageously, locating the inlet 41 at or near the top ofthe tank housing 40 causes an overall movement of water downwardlythrough the tank housing 40 towards filter unit 1 which aids removal ofparticulates and other foreign matter from the mesh 13 and speeds upsettling of the debris in sump 43. In addition, the conical shape of thesump 43 aids downward movement of the debris towards the bottom drainline 44.

[0055] The filter unit assembly may be either gravity-fed or an activelypumped filtration assembly. Either due to the force of gravity or due tothe action of the active pumping, water is passed through the tankhousing 40 and filter unit 1 by entering through mesh 13 and exitingthrough outlet 15 into the outlet pipe 42.

[0056] At the same time, pump 17 is operated to pump water solelythrough rotor 14. The water pumped by pump 17 originates from within thefilter chamber 9 and is therefore free of any particulates or otherforeign matter larger than the aperture size of the mesh 13. Water ispumped into the pump 17 via the inlet aperture 32 in the lower cover 12and pumped out of the pump outlet aperture 31 only into the inletconduit 19 and rotor shaft 21. The pumped water is then forced alongboth arms of the rotor arm 22 and out of the rotor outlets 29 of rotornozzles 23. Due to the angle a of the outlets 29 of the rotor nozzles23, the outflowing water causes the rotor arm 22 to rotate. The wateroutflowing from the rotor outlets 29 is directed against an interiorface of the mesh 13 before passing therethrough. This flow of watercauses particulates and other foreign matter lodged on the outerexterior face of the mesh 13 to be dislodged and to fall away from themesh 13 into sump 43. Periodically the bottom drain line 44 is opened toremove the collected waste material.

[0057] Advantageously, since the flow of water through the rotor 14 isnot taken from the outlet 42, operation of the rotor 14 does not producea decrease in the volumetric flow rate or efficiency of the filter unit1.

[0058] A modified type of tank housing 540 is shown in FIG. 13a in whicha plate, insert or partition 511 is located. The filter unit 1 ispositioned such that its mid-point is level with the partition 511. Anorifice 512 is provided in the partition 511 in which the filter unit 1is located. The partition 511 promotes downward flow within the tankhousing 540 due, in part, to the pressure gradient across the partitiondue to a venturi effect. The downward flow helps the settling of solidsin the sump of the tank housing 540 and also helps prevent the waterbelow the partition 511 being disturbed by the water entering the tankhousing through the inlet. Further, the partition 511 ensures that thewater entering the tank is directed towards the mesh 13 of the filterunit 1 for filtration.

[0059] For maximum efficiency, the radius of the orifice 512 has beenfound to be as follows:

R ₀={square root}{square root over ( )}((πr ²+3η)/π)

[0060] where

[0061] R₀=radius of orifice

[0062] r=radius of filter in centimetres and

[0063] η=flow rate through filter in litres.

[0064] This formula can also be used to determine the radius of the tankhousing in the version shown in FIG. 13, for example.

[0065] Another variant of the tank housing is shown in FIG. 13b. In thisvariant the function of the partition 511 has been incorporated as partof the internal shape of the housing itself. An upper region 515 of thehousing is frusto-conical in shape. A lower region 516 is cylindrical inshape. The junction between the upper region 515 and the lower region516 is located level with the mid-point of the filter unit 1. This hasthe same effect as in the previously described variant of creating apressure gradient which encourages downward flow of water within thetank housing.

[0066] In addition, the tank housing comprises a sump 517 which has amuch reduced cross-sectional area. This has the result of reducing theamount of water which must be emptied fro the tank housing when clearingthe sump 517. In addition, the water exiting the sump 517 into drainline 518 will speed up due to the restriction in diameter. The highvelocities produced ensure that all the collected debris is efficientlyremoved whilst only using a small volume of water.

[0067]FIG. 14 show a second type of tank housing 40′ in which the filterunit 1 may be installed. This type of installation occurs typicallywhere an already fitted ‘vortex’ type filter unit is converted tooperate with the filter unit 1 of the present invention. Theinstallation shows how the filter unit 1 may be orientated upside-downwithout impairing performance. The inlet 41′ is also provided with a 90degree elbow pipe 50 to move the effective inlet 51 of the tank housing40′ to at or near the top of the housing. It has been found thatincreased performance of the filter unit 1 occurs where the tank housing40′ is filled in a non-vortex producing manner such that the inflowingwater fills the tank housing 40′ from the bottom up without asignificant water flow in the radial or tangential directions. However,the filter unit 1 may be used in a vortex tank housing.

[0068]FIG. 15 illustrates a third type of tank housing 40″ in which thefilter unit 1 of the present invention may be installed. The outlet 42″of the tank housing 40″ is provided with a secondary pump 54 separatefrom the dedicated pump 17 of the filter unit 1. The secondary pump 54operates to drive water through the tank housing 40″. The figure alsoillustrates how biological filtering or cleaning stages 55 my bearranged in series with the filter unit assembly of the presentinvention to form an integrated filtration system.

[0069]FIG. 16 illustrates a further embodiment of the present inventionwherein a plurality of the filter unit assemblies are arranged in avertical stack formation. The outlet 15 of the uppermost filter unit 1is connected to the inlet 41 of the next lowermost tank housing 40 andso on down to the lowermost filter unit 1 whose outlet 15 is connectedto the outlet of the filtration system. Preferably the aperture size ofthe meshes 13 in the filter units 1 decreases down the stack from a meshsize of 100 microns or greater in the uppermost filter unit to a meshsize of 25 microns or less in the lowermost filter unit. In this way aprogressive filtration system is provided.

[0070] Adjacent filter unit assemblies may advantageously be joinedsealingly with one another with the provision of gaskets or O-ring seals60. Of course the successive filter unit assemblies may be arrangedotherwise than in a vertical formation; for example, they may bearranged horizontally where the filtration system is actively pumped.

[0071]FIG. 17 shows a further embodiment of filter unit assembly inaccordance with the present invention. The filter unit assembly 110comprises a tank 112. The tank has an inlet 114 and an outlet 118. Afilter unit 1 is located in the tank. Water entering the tank must passthrough the filtration unit in order to leave the tank 112 through theoutlet 118. A lower portion of the tank forms a sump 120 which taperstowards an outlet 122 and a drainage pipe 124.

[0072] The filter unit 1 may be as described in any of the aboveembodiments. Alternatively, another type of filter unit may be used intank 112.

[0073] A drainage pipe 124 is connected to the outlet 122 of the sump120 and is arranged with an outlet or vent to atmosphere 140 at a levelhigher than the level of the inlet 114 into the tank 112. This ensuresthat the head of water in the drainage pipe 124 is greater than that inthe tank 112. Thus, water entering the tank 112 does not simply drainaway, cutting off supply to the outlet 118.

[0074] However, the outlet 122 from the sump 120 to the drainage pipe124 may also be closed by a valve 134 of any suitable type such as agate valve or ball valve.

[0075] A pump 136 is provided to pump water and accumulated debriswhenever desired (and when the valve 134 is open, if provided) from thesump 120 and along the drainage pipe 124 to waste. The pump may be ofany suitable type which is able to operate without fouling due to thedebris which may be present in the water.

[0076] The valve 134 (if present) and pump 136 are operated by aprogrammable controller 138 which includes a time clock and which can bepreset to activate the valve and pump at desired intervals and for adesired length of time. For example, a conventional domestic centralheating timer can be used.

[0077] The controller can be set to operate the valve 134 and pump 136as often as necessary and for as long as necessary. For example, whenthe system is newly installed and the water to be filtered isparticularly laden with particulates and other foreign matter, it may benecessary to clear the accumulated debris every two hours or so,operating the pump for, say, ten minutes each time. Once this initialfiltration has occurred, ongoing filtration may require a lowerfrequency of perhaps twice a day.

[0078]FIG. 17a shows one variant of tank housing having a sump 120 whichcan be automatically emptied. The emptying of the sump 120 is controlledby the pressure of the dedicated pump 132 of the filter unit 1. Thevalve 134 connected to the drain line 124 is held shut by the waterpressure from the pump 132 via a transfer means 146. The valve 134 canonly open when the pump 132 is switched off. Opening of the valve 134 iscaused by action of a spring 147 located in the valve 134. The switchingof the pump 132 can be controlled by a timing means such as a segmentedtime switch 148.

[0079]FIG. 17b shows an alternative arrangement in which a pump 136 isconnected to the drain point. The operating times of the pump 136 arecontrolled by a timing means such as a segmented time switch 148. Theoutlet of the pump 136 is connected to an upstanding U-bend pipe 149 toprevent drainback of waste water.

[0080] It will be apparent that a number of modifications may be made tothis embodiment without departing from the scope of the invention. Forexample, a different type of filtration unit may be used. A filtrationsystem comprising a number of tanks and filtration units through whichwater passes consecutively may be employed, with each tank including asump and automated discharge system in accordance with the invention.

[0081] Variations to any of the embodiments described above may be madewithout departing from the scope of the present invention. For example,the filter unit 1 may be provided with a rotor 14 having only a singleoutlet 29 or more than two outlets 29. The pump 17 may be providedremote from the filter unit 1 rather than being attached thereto. In thecase of multiple filter units 1, a single pump 17 may be used to supplywater to all the rotors 14. The mesh 13 has been described as made ofstainless steel. However, other materials such as heavy duty plastic maybe utilised.

[0082] The rating of the dedicated pump 17 may be varied depending onthe aperture size of the mesh 13. For example, it may be preferred touse a pump such as the ‘Oase USP60’.

[0083] Another variation which may be made to the filter unit assembliesof the above embodiments is the provision of a timer switch so as toenable operation of the rotor 14 and pump 17 at periodic intervals asopposed to continuous operation. This has the advantage that theapparatus uses less power. In addition, with the pump 17 switched off,the mesh 13 starts to become blocked by particles in the water. As itdoes so, the effective aperture size of the mesh 13 decreases leading tothe filtration of smaller particles. When the pump 17 is activated thewater from the rotor 14 tends to remove the solids on the mesh 13 in theform of ‘sheets’ which more readily settle out in the sump of the tankhousing than do individual particles. The periodic operation of pump 17is controlled by a switching means such as a simple timer. Moreadvantageously the operation can be controlled by a float switch in thetank housing where the filter unit assembly is actively pumped. As themesh 13 becomes progressively blocked, the water level in the tankhousing starts to rise which eventually triggers the float switch toturn on the pump 17. Where the filter unit assembly is gravity fed, thefloat switch would be situated in a container downstream of the tankhousing. In this case, blockage of the mesh 13 will lead to reduction inthe water level in the downstream container thus activating the floatswitch and pump 17.

[0084] Where the filter unit assembly is pressurised, a pressure switchmay be used as the switching means.

[0085] Advantageously, a switching relay may be used to coordinateoperation of the pump 17 of the filter unit and the circulatory pump ofthe filtration system such that the general circulatory pump is switchedoff when the dedicated pump of the filter unit is switched on. This hasthe advantage that the water exiting the rotor 14 and impinging on themesh 13 does not have to work against an inflow of water through themesh 13.

[0086]FIG. 18 shows a further embodiment of the present invention inwhich the tank housing 540 is pressurised, in other words the filterunit assembly is part of a closed system which is not open toatmosphere. An air tight lid 545 is provided to seal the filter unitassembly. Alternatively, the tank housing 540 may be made as apressurisable unit. The filter unit 1 and assembly may otherwise be asdescribed in the above embodiments. In particular, the unit 1 may belocated in an orifice formed in a partition 546, and a sump 543 isprovided communicating with a drain line 544. A major advantage of afilter unit assembly which is pressurised is that it may be used in afiltration system that has no loss of head. Such a system is shownschematically in FIG. 19. The output of the filter unit assembly 540inputs into a biological filter stage 560 which then outputs into awater source 570. Water is supplied from the water source 50 to thefilter unit assembly 540 by a circulatory pump 580. Advantageously onlyone pump is required to circulate water round the whole system. Thisdiffers to current systems used in aquaculture where the filtrationstage is non-pressurised. Consequently head is lost at the filtrationstage and therefore another pump is required to move the water throughthe biological filter stage and back to the water source 570.Alternatively, and also disadvantageously, the filtration system has tobe arranged with large vertical displacements between the stages todevelop enough pressure head. The pressurised system of the presentinvention may all be arranged compactly at one level.

[0087] Another variation of the filter unit of the present invention isthe use of a dedicated supply of fluid to the rotor 14 of the filterunit 1. In the embodiments described above, the rotor is supplied withwater by means of dedicated pump 17. Alternatively a different dedicatedsupply may be utilised such as a mains water supply or a source ofotherwise pressurised water. For example, rotor 14 could be plumbed incommunication with a header tank of water having sufficient head toprovide adequate water pressure.

[0088] In a further variation, the rotor 14 may be supplied with adedicated supply of a gas such as air. Air may be used where the mediumbeing filtered is either a gas or a liquid. The rotor gas may be from acompressed gas supply or air powered by an air pump having a rating of100 litres/minute. The source of the gas may be from within the filterunit 1 where the medium being filtered is that gas or alternatively thesource may be external.

[0089] In another variation, the motive force for rotating the rotor 14may be provided by means other than the throughput of fluid though therotor. For example an electric motor may be used or mechanical gearsdriven by the flow of fluid. In this case the nozzles 29 of the rotor donot need to be angled.

[0090] In a further variation, the filter unit 1 may be constructed asshown in FIGS. 3a and 3 b wherein the top cover 11 is removeable simplyby undoing a finger nut 11 a threaded on spindle 21. Once the top cover11 is removed the mesh 13 may be lifted out in one piece for cleaningand/or replacement and the rotor 14 may be accessed.

[0091] Whilst the present invention has been described above in detailfor use with water it is to be understood that it applies equally toother fluids which require filtering such as blood, plasma, wine, air,nitrogen, oxygen etc. The apparatus and method of the present inventionmay be used in many fields, for example, in filtering in medicalapplications, in filtering air for dust extraction or air conditioningeither of a room or in a portable device such as a cleaner. The filtermay also be used to filter water for irrigation, fisheries, hatcheries,swimming pools, baths and ponds in general. For example, using apressurised filtration system as shown in FIG. 18 the present inventionhas found particular application in the extraction of dust, for exampleMDF dust, from air. The filter unit and assemblies of the presentinvention find ready application in a wide range of fields. The aperturesize of the mesh may be adjusted depending on the nature of the mediumbeing filtered. For example, for the filtering of air, an aperture sizedown to 1 micron may be used with no difficulty.

1. A filter unit for filtering particulates and other foreign matterfrom a fluid supply, comprising a filtering chamber, at least a portionof an exterior of the filtering chamber being provided with a meshthrough which fluid may enter the filtering chamber in use, the meshbeing sized to filter particulates and other foreign matter from thefluid, the filter unit further comprising an outlet through whichfiltered fluid exits the filter unit, and a rotatable member locatedwithin the filtering chamber, the rotatable member having at least oneoutlet spaced from an internal face of a mesh, the axis of rotation ofthe rotatable member being such that the at least one outlet traversesat least a substantial portion of the internal face of a mesh, thefilter unit further comprising a dedicated pump having an inletcommunicating with the filtering chamber and an outlet communicatingsolely with the rotatable member such that operation of the pump causesfiltered fluid from within the filtering chamber to be pumped throughthe rotatable member to exit the at least one outlet and impinge on theinternal face of the mesh so as to cause particulates and other foreignmatter located on an external face of the mesh to be dislodged.
 2. Afilter unit as claimed in claim 1, wherein the pump is located remotefrom the filtering chamber.
 3. A filter unit as claimed in claim 1,wherein the pump is attached to the filtering chamber.
 4. A filter unitas claimed in any preceding claim, wherein the pump has a rating ofgreater than 2,000 litres per an hour, preferably, greater than 4,000litres per hour.
 5. A filter unit as claimed in any preceding claim,wherein the rotatable member has two outlets located at opposite ends ofthe rotatable member.
 6. A filter unit as claimed in claim 5, wherein atleast one of the outlets of the rotatable member is angled at between 0°and 90° of a radial direction passing through the axis rotation of therotatable member.
 7. A filter unit as claimed in claim 6, wherein atleast one of the outlets of the rotatable member is angled at between30° and 50° of a radial direction passing through the axis rotation ofthe rotatable member.
 8. A filter unit as claimed in any precedingclaim, wherein at least one outlet of the rotatable member is angled atsubstantially 90° to a radial direction passing through the axisrotation of the rotatable member.
 9. A filter unit as claimed in claim7, wherein at least one of the outlets of the rotatable member is angledat substantially 45° to the radial direction.
 10. A filter unit asclaimed in any preceding claim wherein means are provided to rotate therotor.
 11. A filter unit as claimed in claim 10 wherein the means are anelectric motor.
 12. A filter unit as claimed in claim 10 wherein themeans are mechanical gears driven by a flow of fluid.
 13. A filter unitas claimed in any preceding claim, wherein the mesh has an aperture sizeof less than 1000 microns.
 14. A filter unit as claimed in claim 13,wherein the mesh has an aperture size of approximately 100 microns orless.
 15. A filter unit as claimed in claim 13, wherein the mesh has anaperture size of approximately 10 microns or less.
 16. A filter unit asclaimed in any preceding claim, wherein the mesh is one of a hollanderweave mesh, a wedge wire screen or a plain weave.
 17. A filter unit asclaimed in any preceding claim, wherein the mesh is made of stainlesssteel grade
 316. 18. A filter unit as claimed in any of claims 1 to 16wherein the mesh is made of nylon.
 19. A filter unit as claimed in anypreceding claim, wherein the outlet of the pump communicates with abasal portion of the rotatable member via an inlet conduit.
 20. A filterunit as claimed in any preceding claim, wherein the outlet of the filterunit comprises a flexible sleeve for attaching the outlet to a pipe orother conduit.
 21. A filter unit as claimed in claim 20, wherein thesleeve is made of rubber or similar material.
 22. A filter unit forfiltering particulates and other foreign matter from a fluid supply,comprising a filtering chamber, at least a portion of an exterior of thefiltering chamber being provided with a mesh through which fluid mayenter the filtering chamber in use, the mesh being sized to filterparticulates and other foreign matter from the fluid, the filter unitfurther comprising an outlet through which filtered fluid exits thefilter unit, and a rotatable member located within the filteringchamber, the rotatable member having at least one outlet spaced from aninternal face of a mesh, the axis of rotation of the rotatable memberbeing such that the at least one outlet traverses at least a substantialportion of the internal face of a mesh, the filter unit furthercomprising a dedicated supply of fluid having an outlet communicatingsolely with the rotatable member such that fluid is supplied through therotatable member to exit the at least one outlet and impinge on theinternal face of the mesh so as to cause particulates and other foreignmatter located on an external face of the mesh to be dislodged.
 23. Afilter unit as claimed in claim 22 wherein the dedicated supply of fluidis a source of pressurised water.
 24. A filter unit as claimed in claim23 wherein the water is pressurised by mains pressure.
 25. A filter unitas claimed in claim 23 wherein the water is pressurised by an impeller.26. A filter unit as claimed in claim 23 wherein the water ispressurised by a head of water.
 27. A filter unit as claimed in claim 22wherein the dedicated supply of fluid is a source of pressurised gas.28. A filter unit as claimed in claim 27 wherein the gas is air.
 29. Afilter unit as claimed in claim 28 wherein the air is pressurised by anair pump.
 30. A filter unit assembly comprising a filter unit as claimedin any preceding claim and a tank housing in which the filter unit islocated, the tank housing being provided with an inlet for entry offluid into the tank unit and the outlet of the filter unit forming theoutlet of the tank housing.
 31. A filter unit assembly as claimed inclaim 30 wherein fluid is pumped through the tank housing by a secondarypump separate from the dedicated pump.
 32. A filter unit assembly asclaimed in claim 30, wherein the inlet is orientated so as to create avortex of fluid within the tank housing to aid separation ofparticulates and other foreign matter.
 33. A filter unit assembly asclaimed in claim 32 wherein fluid is fed by gravity through the tankhousing.
 34. A filter unit assembly as claimed in any of claims 30 to33, wherein the tank housing inlet is located at or near a top of thetank housing.
 35. A filter unit assembly as claimed in claim 34, whereinthe tank housing inlet is provided with an elbow so as to deflect fluidentering the tank housing into a direction other than the radial.
 36. Afilter unit assembly as claimed in any of claims 30 to 35 wherein thetank housing comprises a sump in which particulates dislodged from saidfilter unit accumulate.
 37. A filter unit assembly as claimed in any ofclaims 30 to 36 wherein the filter unit is located in an orifice.
 38. Afilter unit assembly as claimed in claim 37 wherein the radius of theorifice is defined by: R ₀={square root}{square root over ( )}((πr²+3η)/π) where R₀=radius of orifice r=radius of filter in centimetresand η=flow rate through filter in litres.
 39. A filter unit assembly asclaimed in any of claims 37 to 38 wherein the orifice is provided in apartition forming a portion of the tank housing.
 40. A filter unitassembly as claimed in any of claims 30 to 39 wherein switching meansare provided for enabling periodic operation of the dedicated pump. 41.A filter unit assembly as claimed in claim 40 wherein the switchingmeans is a timer switch.
 42. A filter unit assembly as claimed in claim40 wherein the switching means is a float switch activatable by thefluid level in the tank housing.
 43. A filter unit assembly as claimedin claim 41 wherein the switching means is a float switch activatable bythe fluid level in a container downstream of the tank housing.
 44. Afilter unit assembly as claimed in any of claims 42 to 43 wherein meansare provided to inhibit entry of fluid into the tank unit when thededicated pump is switched on.
 45. A filter unit assembly as claimed inclaim 44 wherein a circulatory pump of the filtration system is switchedoff when the dedicated pump is switched on.
 46. A filter unit assemblyas claimed in any of claims 30 to 45 which is pressurisable.
 47. Afilter unit assembly as claimed in claim 46 wherein the tank housing isa pressure vessel.
 48. A filtration system comprising one or more filterunits assemblies as claimed in any of claims 30 to
 47. 49. A filtrationsystem as claimed in claim 48, comprising a plurality of filter unitassemblies as claimed in any of claims 30 to 47, wherein the filter unitassemblies are arranged sequentially, wherein the tank housing outlet ofeach filter unit assembly is connected to the tank housing inlet of thesubsequent filter unit assembly or outlet of the filtration system inthe case of the last filter unit assembly.
 50. A filtration system asclaimed in claim 49 wherein the sequential filter unit assemblies arestacked vertically.
 51. A filtration system as claimed in claim 50,wherein a gasket or O-ring seal is provided between adjacent filter unitassemblies.
 52. A filtration system as claimed in any of claims 49 to51, wherein the mesh aperture size of the filter unit in each successivefilter unit assembly decreases in size.
 53. A filtration system asclaimed in claim 52, wherein the mesh aperture size of the first filterunit assembly is 100 microns or greater.
 54. A filtration system asclaimed in any of claims 49 to 53, wherein the mesh aperture size of thelast filter unit assembly is 25 microns or less.
 55. A method offiltering fluid to remove particulates and other foreign mattercomprising the steps of passing the fluid through a filtering chamberhaving a mesh sized to filter the particulates and other foreign matterfrom the fluid, outputting the fluid from the filtering chamber throughan outlet of the filtering chamber, wherein a dedicated pump is used topump fluid from the filtering chamber exclusively through a rotatablemember located within the filtering chamber to exit through at least oneoutlet of the rotatable member to impinge on an interior face of themesh so as to dislodge particulates and other foreign matter located onan exterior face of the mesh.
 56. A method as claimed in claim 55wherein the dedicated pump is operated periodically.
 57. A method asclaimed in claim 56 wherein the dedicated pump is switched on and off byvirtue of the fluid level in the tank housing.
 58. A method as claimedin claim 57 wherein the dedicated pump is switched on and off by virtueof the fluid level in a container downstream of the tank housing.
 59. Afiltration system for filtering particulates and other foreign matterfrom a fluid supply, comprising a tank with an inlet and an outlet, afiltration unit through which fluid must pass to reach the outlet, and asump in which particulates and other foreign matter from the fluidaccumulates, the sump having an outlet, a drainage conduit communicatingwith the outlet, a pump for withdrawing fluid and accumulatedparticulates and other foreign matter through the outlet and dischargingit to a drainage conduit, and a programmable controller for operating avalve and pump.
 60. A filtration system as claimed in claim 59, whereinthe outlet from the sump is provided with a valve.
 61. A filtrationsystem as claimed in claim 60, wherein the valve is a gate valve.
 62. Afiltration system as claimed in claim 60, wherein the valve is a ballvalve.
 63. A filtration system as claimed in any of claims 59 to 62,wherein the controller includes a timer of the type used in centralheating systems.
 64. A filtration system as claimed in any of claims 59to 63, wherein the drainage channel has an outlet or vent to atmosphereat a higher level than the inlet of the tank.
 65. A filtration system asclaimed in any of claims 59 to 64, wherein the filtration unit comprisesa filtering chamber, at least a portion of an exterior of the filteringchamber being provided with a mesh through which fluid may enter thefiltering chamber in use, the mesh being sized to filter particulatesand other foreign matter from the fluid, the filter unit furthercomprising an outlet through which filtered fluid exits the filter unit,and a rotatable member located within the filtering chamber, therotatable member having at least one outlet spaced from an internal faceof a mesh, the axis of rotation of the rotatable member being such thatthe at least one outlet traverses at least a substantial portion of theinternal face of a mesh, the filter unit further comprising a dedicatedpump having an inlet communicating with the filtering chamber and anoutlet communicating solely with the rotatable member such thatoperation of the pump causes filtered fluid from within the filteringchamber to be pumped through the rotatable member to exit the at leastone outlet and impinge on the internal face of the mesh so as to causeparticulates and other foreign matter located on an external face of themesh to be dislodged.
 66. A filter unit as claimed in any of claims 1 to29 wherein the fluid is a liquid.
 67. A filter unit as claimed in claim66 wherein the liquid is in particular one of wine, blood, plasma or afuel.
 68. A filter unit as claimed in any of claims 1 to 29 wherein thefluid is a gas.
 69. A filter unit as claimed in claim 68 wherein the gasis in particular one of air, oxygen, or nitrogen.
 70. A filter unitassembly as claimed in any of claims 30 to 47 wherein the fluid is aliquid.
 71. A filter unit assembly as claimed in claim 70 wherein theliquid is in particular one of wine, blood, plasma or a fuel.
 72. Afilter unit assembly as claimed in any of claims 30 to 47 wherein thefluid is a gas.
 73. A filter unit as claimed in claim 72 wherein the gasis in particular one of air, oxygen, or nitrogen.
 74. A filtrationsystem as claimed in any of claims 48 to 54 or 59 to 65 wherein thefluid is a liquid.
 75. A filtration system as claimed in claim 74wherein the liquid is in particular one of wine, blood, plasma or afuel.
 76. A filtration system as claimed in any of claims 48 to 54 or 59to 65 wherein the fluid is a gas.
 77. A filtration system as claimed inclaim 76 wherein the gas is in particular one of air, oxygen, ornitrogen.
 78. A method as claimed in any of claims 55 to 58 wherein thefluid is a liquid.
 79. A method as claimed in claim 78 wherein theliquid is in particular one of wine, blood, plasma or a fuel.
 80. Amethod as claimed in any of claims 55 to 58 wherein the fluid is a gas.81. A method as claimed in claim 80 wherein the gas is in particular oneof air, oxygen, or nitrogen.